The construction of Pohang Accelerator Laboratory X-ray Free-Electron Laser (PAL-XFEL), a 0.1-nm hard X-ray free-electron laser (FEL) facility based on a 10-GeV S-band linear accelerator (LINAC), is achieved in Pohang, Korea by the end of 2016. The construction of the 1.11 km-long building was completed by the end of 2014, and the installation of the 10-GeV LINAC and undulators started in January 2015. The installation of the 10-GeV LINAC, together with the undulators and beamlines, was completed by the end of 2015. The commissioning began in April 2016, and the first lasing of the hard X-ray FEL line was achieved on 14 June 2016. The progress of the PAL-XFEL construction and its commission are reported here.

The X-ray free-electron laser of the Pohang Accelerator Laboratory (PAL-XFEL) was opened to users in 2017. Since then, significant progress has been made in PAL-XFEL operation and beamline experiments. This includes increasing the FEL pulse energy, increasing the FEL photon energy, generating self-seeding FEL, and trials of two-color operation. In the beamline, new instruments or endstations have been added or are being prepared. Overall, beamline operation has been stabilized since its initiation, which has enabled excellent scientific results through efficient user experiments. In this paper, we describe details of the recent progress of the PAL-XFEL.

We designed a 20-MV S-band traveling-wave deflecting structure to measure the bunch length of the electron beams for the PAL-XFEL. Since the start of commissioning of all RF systems of the PAL-XFEL on 12 April 2016, two out of three fabricated structures are currently being operated; one each in the hard X-ray and the soft X-ray branches. These deflecting structures were carefully tuned by using a 4-m-long nodal phase scanner in a precisely temperature and humidity controlled cleanroom considering the phase predictions calculated using RF field solvers. We carried out RF conditioning and beam commissioning with highly-stable high-power S-band RF systems and an EPICS-based control system. We briefly present our design of S-band deflecting structure and discuss the test results, including the results of the RF and the beam measurements.

We designed a fuse opening switch for the purpose of generation of high voltage pulses. The fuse opening switch was made with copper foil. The fuse opening switch was tested at a capacitor powered circuit discharged by a high current triggered vacuum switch. The experimental results were compared with simple numerical calculations. We measured several electrical parameters for a circuit composed of the fuse opening switch, a pulse transformer, and a peaking switch.